Typescript check the function input parameters if they contain same properties

Question

I need a function that takes two objects A and B and returns a string.

However, the properties of A and B should be all unique: no property should be in both objects. And I want the compiler to typecheck that for me.

myFunction({a:1}, {b:1, c:1}) // Should be OK
myFunction({a:1}, {a:1, b:1, c:1}) // Should NOT be OK, since both objects contain "a"

This is what I got so far, but I run into Type parameter 'B' has a circular constraint.ts(2313) error.

type Exclude<T, U> = T extends U ? never : U

function myFunction<A,  B extends Exclude<A,B>,>(a:A, b:B) : Exclude<A,B> {
  // do something with a and b here 
  return 's' as any // would be nice if I don't need to cast here
}

const x = myFunction({a:1}, {a:1}) // Should produce an typescript error

Any ideas?

Answer 1

so i got it working (partly):

type Exclude<A, U> = U extends A ? never : U;

function myFunction<
  T extends object,
  U extends Exclude<T, P>,
  P extends object = U
>(a: T, b: U) {
  return "something";
}

myFunction({ a: 1 }, { a: 1 }); // Error
myFunction({ a: 1 }, { b: 1 }); // OK

https://codesandbox.io/s/quirky-davinci-72nvqs?file=/src/index.ts